The search for new therapeutic agents has been greatly aided in recent years by a better understanding of the structure of enzymes and other biomolecules associated with diseases. One important class of enzymes that has been the subject of extensive study is protein kinases.
Protein kinases constitute a large family of structurally related enzymes that are responsible for the control of a variety of signal transduction processes within the cell. (See, Hardie, G. and Hanks, S. The Protein Kinase Facts Book, I and II, Academic Press, San Diego, Calif.: 1995). Protein kinases are thought to have evolved from a common ancestral gene due to the conservation of their structure and catalytic function. Almost all kinases contain a similar 250-300 amino acid catalytic domain. The kinases may be categorized into families by the substrates they phosphorylate (e.g., protein-tyrosine, protein-serine/threonine, lipids, etc.). Sequence motifs have been identified that generally correspond to each of these kinase families (See, for example, Hanks, S. K., Hunter, T., FASEB J. 1995, 9, 576-596; Knighton et al., Science 1991, 253, 407-414; Hiles et al., Cell 1992, 70, 419-429; Kunz et al., Cell 1993, 73, 585-596; Garcia-Bustos et al., EMBO J. 1994, 13, 2352-2361).
In general, protein kinases mediate intracellular signaling by effecting a phosphoryl transfer from a nucleoside triphosphate to a protein acceptor that is involved in a signaling pathway. These phosphorylation events act as molecular on/off switches that can modulate or regulate the target protein biological function. These phosphorylation events are ultimately triggered in response to a variety of extracellular and other stimuli. Examples of such stimuli include environmental and chemical stress signals (e.g., osmotic shock, heat shock, ultraviolet radiation, bacterial endotoxin, and H2O2), cytokines (e.g., interleukin-1 (IL-1) and tumor necrosis factor α (TNF-α)), and growth factors (e.g., granulocyte macrophage-colony-stimulating factor (GM-CSF), and fibroblast growth factor (FGF)). An extracellular stimulus may affect one or more cellular responses related to cell growth, migration, differentiation, secretion of hormones, activation of transcription factors, muscle contraction, glucose metabolism, control of protein synthesis, and regulation of the cell cycle.
Many diseases are associated with abnormal cellular responses triggered by protein kinase-mediated events as described above. These diseases include, but are not limited to, cancer and other proliferative disorders. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors that are effective as therapeutic agents.
The c-Met proto-oncogene encodes the Met receptor tyrosine kinase. The Met receptor is a 190 kDa glycosylated dimeric complex composed of a 50 kDa alpha chain disulfide-linked to a 145 kDa beta chain. The alpha chain is found extracellularly while the beta chain contains transmembrane and cytosolic domains. Met is synthesized as a precursor and is proteolytically cleaved to yield mature alpha and beta subunits. It displays structural similarities to semaphorins and plexins, a ligand-receptor family that is involved in cell-cell interaction. The ligand for Met is hepatocyte growth factor (HGF), a member of the scatter factor family and has some homology to plasminogen [Longati, P. et al., Curr. Drug Targets 2001, 2, 41-55); Trusolino, L. and Comoglio, P. Nature Rev. Cancer 2002, 2, 289-300].
Met functions in tumorigenesis and tumor metastasis. Chromosomal rearrangements forming Tpr-met fusions in an osteoclast cell line resulted in constitutively active Met receptors and transformation (Cooper, C. S. et al., Nature 1984, 311, 29-33). Met mutants exhibiting enhanced kinase activity have been identified in both hereditary and sporadic forms of papillary renal carcinoma (Schmidt, L. et al., Nat. Genet. 1997, 16, 68-73; Jeffers, M. et al., Proc. Nat. Acad. Sci. 1997, 94, 11445-11500). Expression of Met along with its ligand HGF is transforming, tumorigenic, and metastatic (Jeffers, M. et al., Oncogene 1996, 13, 853-856; Michieli, P. et al., Oncogene 1999, 18, 5221-5231). HGF/Met has been shown to inhibit anoikis, suspension-induced programmed cell death (apoptosis), in head and neck squamous cell carcinoma cells. Anoikis resistance or anchorage-independent survival is a hallmark of oncogenic transformation of epithelial cells (Zeng, Q. et al., J. Biol. Chem. 2002, 277, 25203-25208).
MET is overexpressed in a significant percentage of human cancers and is amplified during the transition between primary tumors and metastasis. To investigate whether this oncogene is directly responsible for the acquisition of the metastatic phenotype, Giordano et al. exploited a single-hit oncogenic version of MET that was able to transform and to confer invasive and metastatic properties to nontumorigenic cells, both in vitro and in nude mice. They found a point mutation in the signal transducer docking site of MET that increased the transforming ability of the oncogene, but abolished its metastatic potential. They concluded that the metastatic potential of the MET oncogene relies on the properties of its multifunctional docking site, and that a single point mutation affecting signal transduction can dissociate neoplastic transformation from metastasis. Giordano, S., et al., Proc. Nat. Acad. Sci. 94: 13868-13872, 1997.
c-Met is implicated in various cancers, especially renal. It was found that the beta-subunit of the c-Met protooncogene product is the cell-surface receptor for hepatocyte growth factor. It was also identified that the hepatocyte growth factor receptor is the c-met proto-oncogene product. Bottaro, D. P., et al., Science 251: 802-804, 1991.
The nexus between c-Met and colorectal cancer has also been established. Analysis of cMet expression during colorectal cancer progression showed that 50% of the carcinoma specimens analyzed expressed 5-50-fold higher levels of cMet mRMA transcripts and protein versus the adjacent normal colonic mucosa. In addition, when compared to the primary tumor, 70% of colorectal cancer liver metastasis showed cMet over expression. See Long et al., Met Receptor Overexpression and Oncogenic Ki-ras Mutation Cooperate to Enhance Tumorigenicity of Colon Cancer Cells in Vivo. Mol Cancer Res. 2003 March; 1(5): 393-401; Fujisaki, et al., CD44 stimulation induces integrin-mediated adhesion of colon cancer cell lines to endothelial cells by up-regulation of integrins and c-Met and activation of integrins. Cancer Res. 1999 Sep. 1; 59(17): 4427-34; Hiscox et al., Association of the HGF/SF receptor, c-met, with the cell-surface adhesion molecule, E-cadherin, and catenins in human tumor cells. Biochem Biophys Res Commun. 1999 Aug. 2; 261(2): 406-11; Herynk et al., Activation of c-Met in colorectal carcinoma cells leads to constitutive association of tyrosine-phosphorylated beta-cateninz. Clin Exp Metastasis. 2003; 20(4): 291-300; Wielenga et al., Expression of c-Met and heparan-sulfate proteoglycan forms of CD44 in colorectal cancer. Am J Pathol. 2000 November; 157(5): 1563-73; Di Renzo et al., Overexpression and amplification of the Met/HGF receptor gene during the progression of colorectal cancer. Clin. Cancer Res., 1: 147-154, 1995; and Mao, et al., Activation of c-Src by receptor tyrosine kinases in human colon cancer cells with high metastatic potential. Oncogene, 15: 3083-3090, 1997.
The c-Met is also implicated in glioblastoma. High-grade malignant gliomas are the most common cancers of the central nervous system. Despite treatment with surgical resection, radiation therapy, and chemotherapy, the mean overall survival is<1.5 years, and few patients survive for>3 years. A common reason for treatment failure is their innate resistance to radiation and chemotherapy.
Glioblastoma multiforme is the most common and most malignant glial neoplasm. Despite very aggressive treatment, these malignant gliomas are associated with an average life expectancy of only 9 months. The formation and malignant progression of human gliomas are complex processes and involve genetic mutations, chromosomal multiploidy, and aberrant epigenetic influences of multiple mitogens and angiogenic factors.
Human malignant gliomas frequently express both HGF and cMet, which can establish an autocrine loop of biological significance. Glioma cMet expression correlates with glioma grade, and an analysis of human tumor specimens showed that malignant gliomas have a 7-fold higher HGF content than low-grade gliomas.
Gliomas represent the most common form of primary central nervous system malignancy and are among the tumors most tightly linked with HGF-cMet signaling abnormalities. Multiple studies have demonstrated that human gliomas frequently co-express HGF and cMet and that high levels of expression are associated with malignant progression. HGF gene transfer to glioma cell lines enhances tumorigenicity, tumor growth, and tumor-associated angiogenesis. It has also been shown that blocking HGF-cMet signaling reverses these phenotypes in vivo. It was further shown that HGF-cMet is able to activate Akt and protect glioma cell lines from apopototic death, both in vitro and in vivo.
See Hirose et al., Clinical importance of cMet protein expression in high grade astrocytic tumors. Neurol. Med.-Chir. 38:851-859, 1998; Hirose et al., Immunohistochemical examination of cMet protein expression in astrocytic tumors. Acta Neuropathol. 95: 345-351, 1998; Koochekpour et al., Met and hepatocyte growth factor expression in human gliomas. Cancer Res. 57: 5391-5398; Laterra et al., HGF expression enhances human glioblastoma tumorigenicity and growth. Biochem. Biophys. Res. Commun. 235:743-747; Moriyama et al., Concomitant expression of hepatocyte growth factor, HGF activator and cMet genes in human glioma cells in vitro. FEBs Lett. 372:78-82, 1995; Nabeshima et al., Expression of cMet correlates with grade of malignancy in human astrocytic tumors: an immunohistochemical study. Histopathology 31: 436-443, 1997; Shiota et al., Coexpression of hepatocyte growth factor and its receptor (cMet) in HGL4 glioblastoma cells. Lab. Investig. 53: 511-516, 1996; Welch et al., Hepatocyte growth factor and receptor (cMet) in normal and malignant astrocytic cells. Anticancer Res. 19:1635-1640, 1999; Bowers et al., HGF protects against cytoxic death in human glioblastoma via PI3-K and Akt-dependent pathways. Cancer Res. 60:4277-4283, 2000.
It was shown that the effect of NK4 (HGF antagonist), on HGF-promoted growth of a human breast cancer resulted in the reduction of tumor invasiveness and motility, weight and volume. Furthermore, in the in-vitro invasion assay and migration assay, both HGF and human fibroblasts, which secrete bioactive HGF, increased the invasiveness and migration of the breast cancer cells (MDA MB 231). See Growth and angiogenesis of human breast cancer in a nude mouse tumour model is reduced by NK4, the HGF antagonist. Carcinogensis, May 9, 2003. Furthermore, transgenic mice harboring mutationally activated cMet developed metastic mammary carcinoma. These same activating mutants were able to establish tumors in nude mouse NIH 3T3 xenografts (PNAS, Vol 95, pp 14417-14422, November 1998).
Transgenic mice that overexpressed cMet in hepatocytes developed heptocellular carcinoma (HCC) one of the human tumors in which cMet has been implicated previously. Inactivation of the transgene led to regression of even highly advanced tumors, apparently mediated by apoptosis and cessation of cellular proliferation. Numerous cells were proliferating in the liver tumors that were elicited by cMet. Removal of the stimulus from the transgenic hMet led to prompt cessation of cellular proliferation even in the cells of advanced malignancies (The Journal of Cell Biology, Vol. 153, 2001, p. 1023-1033).
HGF/Met signaling is involved in cell adhesion and motility in normal cells and plays a major role in the invasive growth that is found in most tissues, including cartilage, bone, blood vessels, and neurons (reviewed in Comoglio, P. M. and Trusolino, L. J. Clin. Invest. 2002, 109, 857-862). Dysfunctional activation or increased numbers of Met is likely to contribute to the aberrant cell-cell interactions that lead to migration, proliferation, and survival of cells that is characteristic of tumor metastasis. Activation of Met induces and sustains a variety of tumors [Wang, R. et al., J. Cell. Biol. 2001, 153, 1023-1034; Liang, T. J. et al., J. Clin. Invest. 1996, 97, 2872-2877; Jeffers, M. et al., Proc. Nat. Acad. Sci. 1998, 95, 14417-14422] while loss of Met inhibits growth and invasiveness of tumor cells [Jiang, W. G. et al., Clin. Cancer Res. 2001, 7, 2555-2562; Abounader, R. et al., FASEB J. 2002 16, 108-110]. Increased expression of Met/HGF is seen in many metastatic tumors including colon (Fazekas, K. et al., Clin. Exp. Metastasis 2000, 18, 639-649), breast (Elliott, B. E. et al., 2002, Can. J. Physiol. Pharmacol. 80, 91-102), prostate (Knudsen, B. S. et al., Urology 2002, 60, 1113-1117), lung (Siegfried, J. M. et al., Ann. Thorac. Surg. 1998, 66, 1915-1918), and gastric (Amemiya, H. et al., Oncology 2002, 63, 286-296).
Further demonstration of the role Met plays in metastasis was shown by Giordano, et al. (2002) who presented evidence for cross-talk between the semaphorin 4D (SEMA4D; 601866) receptor, plexin B1 (PLXNB1; 601053), and MET during invasive growth in epithelial cells. Binding of SEMA4D to PLXNB1 stimulated tyrosine kinase activity of MET, resulting in tyrosine phosphorylation of both receptors. This effect was not found in cells lacking MET expression. Giordano, S., et al.: The Semaphorin 4D receptor controls invasive growth by coupling with Met. Nature Cell Biol. 4: 720-724, 2002.
HGF-Met signaling has also been associated with increased risk of atherosclerosis (Yamamoto, Y. et al., J. Hypertens. 2001, 19, 1975-1979; Morishita, R. et al., Endocr. J. 2002, 49, 273-284) and increased fibrosis of the lung (Crestani, B. et al., Lab. Invest. 2002, 82, 1015-1022.
Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase comprised of a and b isoforms that are each encoded by distinct genes [Coghlan et al., Chemistry & Biology, 7, 793-803 (2000); Kim and Kimmel, Curr. Opinion Genetics Dev., 10, 508-514 (2000)]. GSK-3 has been implicated in various diseases including diabetes, Alzheimer's disease, CNS disorders such as manic depressive disorder and neurodegenerative diseases, and cardiomyocyte hypertrophy [see, e.g., WO 99/65897; WO 00/38675; Kaytor and Orr, Curr. Opin. Neurobiol., 12, 275-8 (2000); Haq et al., J. Cell Biol., 151, 117-30 (2000); Eldar-Finkelman, Trends Mol. Med., 8, 126-32 (2002)]. These diseases are associated with the abnormal operation of certain cell signaling pathways in which GSK-3 plays a role.
GSK-3 has been found to phosphorylate and modulate the activity of a number of regulatory proteins. These include glycogen synthase, which is the rate-limiting enzyme required for glycogen synthesis, the microtubule-associated protein Tau, the gene transcription factor b-catenin, the translation initiation factor e1F-2B, as well as ATP citrate lyase, axin, heat shock factor-1, c-Jun, c-myc, c-myb, CREB, and CEPBa. These diverse targets implicate GSK-3 in many aspects of cellular metabolism, proliferation, differentiation and development.
In a GSK-3 mediated pathway that is relevant for the treatment of type II diabetes, insulin-induced signaling leads to cellular glucose uptake and glycogen synthesis. GSK-3 is a negative regulator of the insulin-induced signal in this pathway. Normally, the presence of insulin causes inhibition of GSK-3-mediated phosphorylation and deactivation of glycogen synthase. The inhibition of GSK-3 leads to increased glycogen synthesis and glucose uptake [Klein et al., PNAS, 93, 8455-9 (1996); Cross et al., Biochem. J., 303, 21-26 (1994); Cohen, Biochem. Soc. Trans., 21, 555-567 (1993); and Massillon et al., Biochem J. 299, 123-128 (1994); Cohen and Frame, Nat. Rev. Mol. Cell. Biol., 2, 769-76 (2001)]. However, where the insulin response is impaired in a diabetic patient, glycogen synthesis and glucose uptake fail to increase despite the presence of relatively high blood levels of insulin. This leads to abnormally high blood levels of glucose with acute and chronic effects that may ultimately result in cardiovascular disease, renal failure and blindness. In such patients, the normal insulin-induced inhibition of GSK-3 fails to occur. It has also been reported that GSK-3 is overexpressed in patients with type II diabetes [WO 00/38675]. Therapeutic inhibitors of GSK-3 are therefore useful for treating diabetic patients suffering from an impaired response to insulin.
Apoptosis has been implicated in the pathophysiology of ischemic brain damage (Li et al., 1997; Choi, et al., 1996; Charriaut-Marlangue et al., 1998; Grahm and Chen, 2001; Murphy et al., 1999; Nicotera et al., 1999). Recent publications indicate that activation of GSK-3β may be involved in apoptotic mechanisms (Kaytor and Orr, 2002; Culbert et al., 2001). Studies in rat models of ischemic stroke induced by middle cerebral artery occlusion (MCAO) showed increased GSK-3b expression is following ischemia (Wang et al., Brain Res, 859, 381-5, 2000; Sasaki et al., Neurol Res, 23, 588-92,2001). Fibroblast growth factor (FGF) reduced ischemic brain injury after permanent middle cerebral artery occlusion (MCO) in rats (Fisher et al. 1995; Song et al. 2002). Indeed, the neuroprotective effects of FGF demonstrated in ischemia models in rats may be mediated by a PI-3 kinase/AKT-dependent inactivation of GSK-3b (Hashimoto et al., 2002). Thus, inhibition of GSK-3β after a cerebral ischemic event may ameliorate ischemic brain damage.
GSK-3 is also implicated in myocardial infarction. See Jonassen et al., Circ Res, 89: 1191, 2001 (The reduction in myocardial infarction by insulin administration at reperfusion is mediated via Akt dependent signaling pathway); Matsui et al., Circulation, 104: 330, 2001 (Akt activation preserves cardiac function and prevents cardiomyocyte injury after transient cardiac ischemia in vivo); Miao et al., J Mol Cell Cardiol, 32: 2397, 2000 (Intracoronary, adenovirus-mediated Akt gene delivery in heart reduced gross infarct size following ischemia-reperfusion injury in vivo); and Fujio et al., Circulation et al., 101: 660, 2000 (Akt signaling inhibits cardiac myocyte apoptosis in vitro and protects against ischemia-reperfusion injury in mouse heart).
GSK-3 activity plays a role in head trauma. See Noshita et al., Neurobiol Dis, 9: 294, 2002 (Upregulation of Akt/PI3-kinase pathway may be crucial for cell survival after traumatic brain injury) and Dietrich et al., J Neurotrauma, 13: 309, 1996 (Posttraumatic administration of bFGF significantly reduced damaged cortical neurons & total contusion volume in a rat model of traumatic brain injury).
GSK-3 is also known to play a role in psychiatric disorders. See Eldar-Finkelman, Trends Mol Med, 8:126, 2002; Li et al., Bipolar Disord, 4: 137, 2002 (LiCl and Valproic acid, anti-psychotic, mood stabilizing drugs, decrease GSK3 activities and increase beta-catenin) and Lijam et al., Cell, 90: 895, 1997 (Dishevelled KO mice showed abnormal social behavior and defective sensorimotor gating. Dishevelled, a cytoplasmic protein involved in WNT pathway, inhibits GSK3beta activities).
It has been shown that GSK3 inhibition by lithium and valproic acid induces axonal remodeling and change synaptic connectivity. See Kaytor & Orr, Curr Opin Neurobiol, 12: 275, 2002 (Downregulation of GSK3 causes changes in microtubule-associated proteins: tau, MAP1 & 2) and Hall et al., Mol Cell Neurosci, 20: 257, 2002 (Lithium and valproic acid induces the formation of growth cone-like structures along the axons).
GSK-3 activity is also associated with Alzheimer's disease. This disease is characterized by the presence of the well-known b-amyloid peptide and the formation of intracellular neurofibrillary tangles. The neurofibrillary tangles contain hyperphosphorylated Tau protein, in which Tau is phosphorylated on abnormal sites. GSK-3 has been shown to phosphorylate these abnormal sites in cell and animal models. Furthermore, inhibition of GSK-3 has been shown to prevent hyperphosphorylation of Tau in cells [Lovestone et al., Curr. Biol., 4, 1077-86 (1994); and Brownlees et al., Neuroreport 8, 3251-55 (1997); Kaytor and Orr, Curr. Opin. Neurobiol., 12, 275-8 (2000)]. In transgenic mice overexpressing GSK3, significant increased Tau hyperphosphorylation and abnormal morphology of neurons were observed [Lucas et al., EMBO J, 20: 27-39 (2001)]. Active GSK3 accumulates in cytoplasm of pretangled neurons, which can lead to neurofibrillary tangles in brains of patients with AD [Pei et al., J Neuropathol Exp Neurol, 58, 1010-19 (1999)]. Therefore, inhibition of GSK-3 slows or halts the generation of neurofibrillary tangles and thus treats or reduces the severity of Alzheimer's disease.
Evidence for the role GSK-3 plays in Alzheimer's disease has been shown in vitro. See Aplin et al. (1996), J Neurochem 67: 699; Sun et al. (2002), Neurosci Lett 321: 61 (GSK3b phosphorylates cytoplasmic domain of Amyloid Precursor Protein (APP) and GSK3b inhibition reduces Ab40 & Ab42 secretion in APP-transfected cells); Takashima et al. (1998), PNAS 95:9637; Kirschenbaum et al. (2001), J Biol Chem 276:7366 (GSK3b complexes with and phosphorylates presenilin-1, which is associated with gamma-secretase activity in the synthesis of Ab from APP); Takashima et al. (1998), Neurosci Res 31:317 (Activation of GSK3b by Ab(25-35) enhances phosphorylation of tau in hippocampal neurons. This observation provides a link between Ab and neurofibrillary tangles composed of hyperphosphorylated tau, another pathological hallmark of AD); Takashima et al. (1993), PNAS 90:7789 (Blockade of GSK3b expression or activity prevents Ab-induced neuro-degeneration of cortical and hippocampal primary cultures); Suhara et al. (2003), Neurobiol Aging. 24:437 (Intracellular Ab42 is toxic to endothelial cells by interfering with activation of Akt/GSK-3b signaling-dependent mechanism); De Ferrari et al. (2003) Mol Psychiatry 8:195 (Lithium protects N2A cells & primary hippocampal neurons from Ab fibrils-induced cytotoxicity, & reduced nuclear translocation/destabilization of b-catenin); and Pigino et al., J Neurosci, 23:4499, 2003 (The mutations in Alzheimer's presenilin 1 may deregulate and increase GSK-3 activity, which in turn, impairs axonal transport in neurons. The consequent reductions in axonal transport in affected neurons can ultimately lead to neurodegeneration).
Evidence for the role GSK-3 plays in Alzheimer's disease has been shown in vivo. See Yamaguchi et al. (1996), Acta Neuropathol 92: 232; Pei et al. (1999), J Neuropath Exp Neurol 58: 1010 (GSK3b immunoreactivity is elevated in susceptible regions of AD brains); Hernandez et al. (2002), J Neurochem 83: 1529 (Transgenic mice with conditional GSK3b overexpression exhibit cognitive deficits similar to those in transgenic APP mouse models of AD); De Ferrari et al. (2003) Mol Psychiatry 8:195 (Chronic lithium treatment rescued neurodegeneration and behavioral impairments (Morris water maze) caused by intrahippocampal injection of Ab fibrils.); McLaurin et al., Nature Med, 8:1263, 2002 (Immunization with Ab in a transgenic model of AD reduces both AD-like neuropathology and the spatial memory impairments); and Phiel et al. (2003) Nature 423:435 (GSK3 regulates amyloid-beta peptide production via direct inhibition of gamma secretase in AD tg mice).
Presenilin-1 and kinesin-1 are also substrates for GSK-3 and relate to another mechanism for the role GSK-3 plays in Alzheimer's disease, as was recently described by Pigino, G., et al., Journal of Neuroscience (23: 4499, 2003). It was found that GSK3beta phosphorylates kinesin-I light chain, which results in a release of kinesin-1 from membrane-bound organelles, leading to a reduction in fast anterograde axonal transport (Morfini et al., 2002). The authors suggest that the mutations in PS1 may deregulate and increase GSK-3 activity, which in turn, impairs axonal transport in neurons. The consequent reductions in axonal transport in affected neurons ultimately lead to neurodegeneration.
GSK-3 is also associated with amyotrophic lateral sclerosis (ALS). See Williamson and Cleveland, 1999 (Axonal transport is retarded in a very early phase of ALS in mSOD1 mice); Morfini et al., 2002 (GSK3 phosphorylates kinesin light chains and inhibit anterograde axonal transport); Warita et al., Apoptosis, 6: 45, 2001 (The majority of spinal motor neurons lost the immunoreactivities for both PI3-K and Akt in the early and presymptomatic stage that preceded significant loss of the neurons in this SOD1 tg animal model of ALS); and Sanchez et al., 2001 (The inhibition of PI-3K induces neurite retraction mediated by GSK3 activation).
GSK-3 activity is also linked to spinal cord and peripheral nerve injuries. It has been shown that GSK3 inhibition by lithium and valproic acid can induce axonal remodeling and change synaptic connectivity. See Kaytor & Orr, Curr Opin Neurobiol, 12: 275, 2002 (Downregulation of GSK3 causes changes in microtubule-associated proteins: tau, MAP1 & 2) and Hall et al., Mol Cell Neurosci, 20: 257, 2002 (Lithium and valproic acid induces the formation of growth cone-like structures along the axons). See also Grothe et al., Brain Res, 885: 172, 2000 (FGF2 stimulate Schwann cell proliferation and inhibit myelination during axonal growth); Grothe and Nikkhah, 2001 (FGF-2 is up regulated in the proximal and distal nerve stumps within 5 hours after nerve crush); and Sanchez et al., 2001 (The inhibition of PI-3K induces neurite retraction mediated by GSK3 activation).
Another substrate of GSK-3 is b-catenin, which is degraded after phosphorylation by GSK-3. Reduced levels of b-catenin have been reported in schizophrenic patients and have also been associated with other diseases related to increase in neuronal cell death [Zhong et al., Nature, 395, 698-702 (1998); Takashima et al., PNAS, 90, 7789-93 (1993); Pei et al., J. Neuropathol. Exp, 56, 70-78 (1997); and Smith et al., Bio-org. Med. Chem. 11, 635-639 (2001)]. Furthermore, b-catenin and Tcf-4 play a dual role in vascular remodeling by inhibiting vascular smooth muscle cell apoptosis and promoting proliferation (Wang et al., Circ Res, 90: 340, 2002). Accordingly, GSK-3 is associated with angiogenic disorders. See also Liu et al., FASEB J, 16: 950, 2002 (Activation of GSK3 reduces hepatocyte growth factor, leading to altered endothelial cell barrier function and diminished vascular integrity) and Kim et al., J Biol Chem, 277: 41888, 2002 (GSK3beta activation inhibits angiogenesis in vivo using Matrigel plug assay: the inhibition of GSK3beta signaling enhances capillary formation).
Association between GSK-3 and Huntington's disease has been shown. See Carmichael et al., J. Biol. Chem., 277: 33791, 2002 (GSK3beta inhibition protect cells from poly-glutamine-induced neuronal and non-neuronal cell death via increases in b-catenin and its associated transcriptional pathway). Overexpression of GSK3 reduced the activation of heat shock transcription factor-1 and heat shock protein HSP70 (Bijur et al., J Biol Chem, 275: 7583, 2000) that are shown to decrease both poly-(Q) aggregates and cell death in in vitro HD model (Wyttenbach et al., Hum Mol Genet, 11: 1137, 2002).
GSK-3 effects the levels of FGF-2 and their receptors are increased during remyelination of brain aggregate cultures remyelinating rat brains. See Copelman et al., 2000, Messersmith, et al., 2000; and Hinks and Franklin, 2000. It was also found that FGF-2 induces process outgrowth by oligodendrocytes implicating involvement of FGF in remyelination (Oh and Yong, 1996; Gogate et al., 1994) and that FGF-2 gene therapy has shown to improve the recovery of experimental allergic encephalomyelitis (EAE) mice (Ruffini, et al., 2001).
GSK-3 has also been associated with hair growth because Wnt/beta-catenin signaling is shown to play a major role in hair follicle morphogenesis and differentiation (Kishimotot et al. Genes Dev, 14:1181, 2000; Millar, J Invest Dermatol, 118:216, 2002). It was found that mice with constitutive overexpression of the inhibitors of Wnt signaling in skin failed to develop hair follicles. Wnt signals are required for the initial development of hair follicles and GSK3 constitutively regulates Wnt pathways by inhibiting beta-catenin. (Andl et al., Dev Cell 2:643, 2002). A transient Wnt signal provides the crucial initial stimulus for the start of a new hair growth cycle, by activating beta-catenin and TCF-regulated gene transcription in epithelial hair follicle precursors (Van Mater et al., Genes Dev, 17:1219, 2003).
Because GSK-3 activity is associated with sperm motility, GSK-3 inhibition is useful as a male contraceptive. It was shown that a decline in sperm GSK3 activity is associated with sperm motility development in bovine and monkey epididymis (Vijayaraghavan et al., Biol Reprod, 54:709, 1996; Smith et al., J Androl, 20:47, 1999). Furthermore, tyrosine & serine/threonine phosphorylation of GSK3 is high in motile compared to immotile sperm in bulls (Vijayaraghavan et al., Biol Reprod, 62:1647, 2000). This effect was also demonstrated with human sperm (Luconi et al., Human Reprod, 16:1931, 2001).
The Janus kinases (JAK) are a family of tyrosine kinases consisting of JAK1, JAK2, JAK3 and TYK2. The JAKs play a critical role in cytokine signaling. The down-stream substrates of the JAK family of kinases include the signal transducer and activator of transcription (STAT) proteins. JAK/STAT signaling has been implicated in the mediation of many abnormal immune responses such as allergies, asthma, autoimmune diseases such as transplant rejection, rheumatoid arthritis, amyotrophic lateral sclerosis and multiple sclerosis as well as in solid and hematologic malignancies such as leukemias and lymphomas. The pharmaceutical intervention in the JAK/STAT pathway has been reviewed [Frank Mol. Med. 5: 432-456 (1999) & Seidel, et al., Oncogene 19: 2645-2656 (2000)].
JAK1, JAK2, and TYK2 are ubiquitously expressed, while JAK3 is predominantly expressed in hematopoietic cells. JAK3 binds exclusively to the common cytokine receptor gamma chain (gc) and is activated by IL-2, IL-4, IL-7, IL-9, and IL-15. The proliferation and survival of murine mast cells induced by IL-4 and IL-9 have, in fact, been shown to be dependent on JAK3- and gc-signaling [Suzuki et al., Blood 96: 2172-2180 (2000)].
Cross-linking of the high-affinity immunoglobulin (Ig) E receptors of sensitized mast cells leads to a release of proinflammatory mediators, including a number of vasoactive cytokines resulting in acute allergic, or immediate (type I) hypersensitivity reactions [Gordon et al., Nature 346: 274-276 (1990) & Galli, N. Engl. J. Med., 328: 257-265 (1993)]. A crucial role for JAK3 in IgE receptor-mediated mast cell responses in vitro and in vivo has been established [Malaviya, et al., Biochem. Biophys. Res. Commun. 257:807-813 (1999)]. In addition, the prevention of type I hypersensitivity reactions, including anaphylaxis, mediated by mast cell-activation through inhibition of JAK3 has also been reported [Malaviya et al., J. Biol. Chem. 274:27028-27038 (1999)]. Targeting mast cells with JAK3 inhibitors modulated mast cell degranulation in vitro and prevented IgE receptor/antigen-mediated anaphylactic reactions in vivo.
A recent study described the successful targeting of JAK3 for immune suppression and allograft acceptance. The study demonstrated a dose-dependent survival of Buffalo heart allograft in Wistar Furth recipients upon administration of inhibitors of JAK3 indicating the possibility of regulating unwanted immune responses in graft versus host disease [Kirken, transpl. proc. 33: 3268-3270 (2001)].
IL-4-mediated STAT-phosphorylation has been implicated as the mechanism involved in early and late stages of rheumatoid arthritis (RA). Up-regulation of proinflammatory cytokines in RA synovium and synovial fluid is a characteristic of the disease. It has been demonstrated that IL-4-mediated activation of IL-4/STAT pathway is mediated through the Janus Kinases (JAK 1 & 3) and that IL-4-associated JAK kinases are expressed in the RA synovium [Muller-Ladner, et al., J. Immunol. 164: 3894-3901 (2000)].
Familial amyotrophic lateral sclerosis (FALS) is a fatal neurodegenerative disorder affecting about 10% of ALS patients. The survival rates of FALS mice were increased upon treatment with a JAK3 specific inhibitor. This confirmed that JAK3 plays a role in FALS [Trieu, et al., Biochem. Biophys. Res. Commun. 267: 22-25 (2000)].
Signal transducer and activator of transcription (STAT) proteins are activated by, among others, the JAK family kinases. Results form a recent study suggested the possibility of intervention in the JAK/STAT signaling pathway by targeting JAK family kinases with specific inhibitors for the treatment of leukemia [Sudbeck, et al., Clin. Cancer Res. 5: 1569-1582 (1999)]. JAK3 specific compounds were shown to inhibit the clonogenic growth of JAK3-expressing cell lines DAUDI, RAMOS, LC1; 19, NALM-6, MOLT-3 and HL-60.
In animal models, TEL/JAK2 fusion proteins have induced myeloproliferative disorders and in hematopoietic cell lines, introduction of TEL/JAK2 resulted in activation of STAT1, STAT3, STAT5, and cytokine-independent growth [Schwaller, et al., EMBO J. 17: 5321-5333 (1998)].
Inhibition of JAK 3 and TYK 2 abrogated tyrosine phosphorylation of STAT3, and inhibited cell growth of mycosis fungoides, a form of cutaneous T cell lymphoma. These results implicated JAK family kinases in the constitutively activated JAK/STAT pathway that is present in mycosis fungoides [Nielsen, et al., Proc. Nat. Acad. Sci. U.S.A. 94: 6764-6769 (1997)]. Similarly, STAT3, STAT5, JAK1 and JAK2 were demonstrated to be constitutively activated in mouse T cell lymphoma characterized initially by LCK over-expression, thus further implicating the JAK/STAT pathway in abnormal cell growth [Yu, et al., J. Immunol. 159: 5206-5210 (1997)]. In addition, IL-6-mediated STAT3 activation was blocked by an inhibitor of JAK, leading to sensitization of myeloma cells to apoptosis [Catlett-Falcone, et al., Immunity 10:105-115 (1999)].
Tyrosine kinases are a class of enzymes that mediate intracellular signal transduction pathways. Abnormal activity of these kinases has been shown to contribute to cell proliferation, carcinogenesis and cell differentiation. Thus, agents that modulate the activity of tyrosine kinases are useful for preventing and treating proliferative diseases associated with these enzymes.
Syk is a tyrosine kinase that plays a critical role in Fc∈RI mediated mast cell degranulation and eosinophil activation. Accordingly, Syk kinase is implicated in various allergic disorders, in particular asthma. It has been shown that Syk binds to the phosphorylated gamma chain of the Fc∈RI receptor via N-terminal SH2 domains and is essential for downstream signaling [Taylor et al., Mol. Cell. Biol. 1995, 15, 4149].
Inhibition of eosinophil apoptosis has been proposed as a key mechanism for the development of blood and tissue eosinophilia in asthma. IL-5 and GM-CSF are upregulated in asthma and are proposed to cause blood and tissue eosinophilia by inhibition of eosinophil apoptosis. Inhibition of eosinophil apoptosis has been proposed as a key mechanism for the development of blood and tissue eosinophilia in asthma. It has been reported that Syk kinase is required for the prevention of eosinophil apoptosis by cytokines (using antisense)[Yousefi et al., J. Exp. Med. 1996, 183, 1407].
The role of Syk in FcgR dependent and independent response in bone marrow derived macrophages has been determined by using irradiated mouse chimeras reconstituted with fetal liver cells from Syk -/- embryos. Syk deficient macrophages were defective in phagocytosis induced by FcgR but showed normal phagocytosis in response to complement [Kiefer et al., Mol. Cell. Biol. 1998, 18, 4209]. It has also been reported that aerosolized Syk antisense suppresses Syk expression and mediator release from macrophages [Stenton et al., J. Immunology 2000, 164, 3790].
KDR is a tyrosine kinase receptor that also binds VEGF (vascular endothelial growth factor) Neufeld et al., 1999, FASEB J., 13, 9. The binding of VEGF to the KDR receptor leads to angiogenesis, which is the sprouting of capillaries from preexisting blood vessels. High levels of VEGF are found in various cancers causing tumor angiogenesis and permitting the rapid growth of cancerous cells. Therefore, suppressing VEGF activity is a way to inhibit tumor growth, and it has been shown that this can be achieved by inhibiting KDR receptor tyrosine kinase. For example, SU5416 is a selective inhibitor of the tyrosine kinase and was reported to also suppress tumor vascularization and the growth of multiple tumors. Fong et al., 1999, Cancer Res. 59, 99. Other inhibitors of KDR tyrosine kinase for the treatment of cancer have also been reported (WO 98/54093, WO 99/16755, WO 00/12089).
Examples of cancers that may be treated by such inhibitors include brain cancer, genitourinary tract cancer, lymphatic system cancer, stomach cancer, cancer of the larynx, lung cancer, pancreatic cancer, breast cancer, Kaposi's sarcoma, and leukemia. Other diseases and conditions associated with abnormal tyrosine kinase activity include vascular disease, autoimmune diseases, ocular conditions, and inflammatory diseases.
A family of type III receptor tyrosine kinases including Flt3, c-Kit, PDGF-receptor and c-Fms play an important role in the maintenance, growth and development of hematopoietic and non-hematopoietic cells. [Scheijen, B, Griffin J D, Oncogene, 2002, 21, 3314-3333 and Reilly, JT, British Journal of Haematology, 2002, 116, 744-757]. FLT-3 and c-Kit regulate maintenance of stem cell/early progenitor pools as well the development of mature lymphoid and myeloid cells [Lyman, S, Jacobsen, S, Blood, 1998, 91, 1101-1134]. Both receptors contain an intrinsic kinase domain that is activated upon ligand-mediated dimerization of the receptors. Upon activation, the kinase domain induces autophosphorylation of the receptor as well as the phosphorylation of various cytoplasmic proteins that help propagate the activation signal leading to growth, differentiation and survival. Some of the downstream regulators of FLT-3 and c-Kit receptor signaling include, PLCγ, PI3-kinase, Grb-2, SHIP and Src related kinases [Scheijen, B, Griffin J D, Oncogene, 2002, 21, 3314-3333]. Both receptor tyrosine kinases have been shown to play a role in a variety of hematopoietic and non-hematopoietic malignancies. Mutations that induce ligand independent activation of FLT-3 and c-Kit have been implicated acute-myelogenous leukemia (AML), acute lymphocytic leukemia (ALL), mastocytosis and gastrointestinal stromal tumor (GIST). These mutations include single amino acid changes in the kinase domain or internal tandem duplications, point mutations or in-frame deletions of the juxtamembrane region of the receptors. In addition to activating mutations, ligand dependent (autocrine or paracrine) stimulation of over-expressed wild-type FLT-3 or c-Kit can contribute to the malignant phenotype [Scheijen, B, Griffin J D, Oncogene, 2002, 21, 3314-3333].
c-fms encodes for macrophage colony stimulating factor receptor (M-CSF-1R) which is expressed predominately in the monocytes/macrophage lineage [Dai, XM et al., Blood, 2002, 99, 111-120]. MCSF-1R and its ligand regulate macrophage lineage growth and differentiation. Like the other family members, MCSF-1R contains an intrinsic kinase domain that is activated upon ligand-induced dimerization of the receptor. MCSF-1R is also expressed in non-hematopoietic cells including mammary gland epithelial cells and neurons. Mutations in this receptor are potentially linked to myeloid leukemias and its expression is correlated with metastatic breast, ovarian and endometrial carcinomas [Reilly, J T, British Journal of Haematology, 2002, 116, 744-757 and Kacinski, B M, Mol. Reprod and Devel., 1997, 46, 71-74]. Another possible indication for antagonists of MCSF-1R is osteoporosis [Teitelbaum, S, Science 2000, 289, 1504-1508.
Aurora-2 is a serine/threonine protein kinase that has been implicated in human cancer, such as colon, breast and other solid tumors. This kinase is involved in protein phosphorylation events that regulate the cell cycle. Specifically, Aurora-2 plays a role in controlling the accurate segregation of chromosomes during mitosis. Misregulation of the cell cycle can lead to cellular proliferation and other abnormalities. In human colon cancer tissue, the aurora-2 protein has been found to be overexpressed [Bischoff et al., EMBO J., 17, 3052-3065 (1998); Schumacher et al., J. Cell Biol., 143, 1635-1646 (1998); Kimura et al., J. Biol. Chem., 272, 13766-13771 (1997)].
Transforming growth factor-beta (TGF-beta) activated kinase 1 (TAK-1) is a 67 kDa ubiquitin-dependent serine-threonine kinase that functions as a mitogen-activated protein (MAP) kinase kinase kinase (MAPKKK or MEKK) (Wang, C., et al., Nature 2001, 412, 346-351).
Originally described as stimulated by TGF-beta superfamily members (Yamaguchi K. et al., Science 1995, 270, 2008-2011) TAK-1 is known to also function in signaling from numerous cell modulators including proinflammatory cytokines. TAK-1 is critical for signaling from IL-1beta/TLR ligands (Holtmann H, et al., J. Biol. Chem. 2001, 276, 3508-3516; Jiang Z, et al., J. Biol. Chem. 2003, 278, 16713-16719) and TNF-alpha (Takaesu G. et al., J. Mol. Biol. 2003, 326, 105-115). In addition TAK-1 plays a role in IL-18 (Wald, D., et al., Eur. J. Immunol. 2001, 31, 3747-3754), RANKL (Mizukami J., et al., Mol. Cell. Biol. 2002, 22, 992-1000) and ceramide (Shirakabe K., et al., J. Biol. Chem. 1997, 272, 8141-8144) signaling.
Through interaction with corresponding cell surface receptors these ligands stimulate TAK-1 to relay signals to a variety of pathways such as IKK/NFkappaB, JNK, and p38, that are important regulators of cellular processes including apoptosis (Edlund S., et al., Mol Biol Cell. 2003, 14, 529-544), differentiation (Suzawa, M. et al., Nat Cell Biol 2003, 5, 224-230), and cell cycle progression (Bradham C A, et al., Am J Physiol Gastrointest Liver Physiol. 2001 281, G1279-89).
Modification of signaling pathways can alter cellular processes and contribute to disease. Due to its central role in signaling from numerous cell surface receptors TAK-1 may be an important therapeutic target for a variety of diseases. The cytokines IL-1beta and TNFalpha are important mediators of inflammation in rheumatoid arthritis and other inflammatory diseases (Maini R N. and Taylor P C. Ann. Rev. Med. 2000, 51, 207-229). TAK-1 may be important in regulating disease-relevant cellular responses in these cases (Hammaker D R, et al. J. Immunol. 2004, 172, 1612-1618). TAK-1 affects cellular fibrotic responses (Ono K., et al., Biochem. Biophys. Res. Commun. 2003, 307, 332-337). It may also plays a role in heart failure (Zhang, D., Nat. Med. 2000, 6, 556-563), osteoporosis (Mizukami J, et al., Mol. Cell. Biol. 2002, 22, 992-1000) and survival of hepatocellular carcinoma cells (Arsura M, et al. Oncogene 2003, 22, 412-425). TAK-1 signaling may affect neurite outgrowth (Yanagisawa M., et al. Genes Cells. 2001, 6, 1091-1099) and is involved in control of adipogenesis (Suzawa M., et al. Nat. Cell. Biol. 2003, 5, 224-230) and cardiomyocyte differentiation (Monzen K., et al. J. Cell. Biol. 2001, 153(4), 687-698.
As a result of the biological importance of protein kinases, there is current interest in therapeutically effective protein kinase inhibitors. Accordingly, there is still a great need to develop inhibitors of protein kinases that are useful in treating various diseases or conditions associated with protein kinase activation. In particular, it would be desirable to develop compounds that are useful as inhibitors of c-Met, GSK3, JAK, SYK, KDR, FLT-3, c-Kit, Aurora, or TAK-1 particularly given the inadequate treatments currently available for the majority of the disorders implicated in their activation.